Interactions of proton and non-proton spins: Contrast in nuclear magnetic resonance spectroscopy and imaging

Nuclear Magnetic Resonance (NMR) provides quantitative techniques to characterize molecular dynamics and interactions. This dissertation explores methods to enhance sensitivity and enrich the information content of NMR experiments using X-1H dipolar and scalar couplings.;Optical pumping increases the signal intensity of 129Xe (termed HypXe) by as much as 104 times Boltzmann polarization levels and successful transfer of this polarization may increase the signal-to-noise ratio of secondary proton spins. The binding of HypXe to molecules decreases the internuclear distance and enhances the 129Xe-1H dipolar cross-relaxation pathways near the binding site. Although alpha-cyclodextrin binds xenon, no 1H-signal enhancement is observed in aqueous solutions of HypXe and alpha-cyclodextrin.;Although 129Xe-1H cross-relaxation is inefficient relative to 1H auto-relaxation pathways, the use of X- 1H spin coupling is explored further as a general mechanism for affecting the information content of 1H images. The results from 23 Na- 1H spin coupling in aqueous saline solutions indicate that the cross-relaxation rate is slow relative to the autorelaxation rate of 23Na and demonstrates that 23Na-1 H population transfer is an inefficient mechanism for generating contrast under physiologic conditions.;Calculations of the bulk-water 1H T2 for solutions of 15N-labeled molecules suggest that the X-1H scalar-coupling interactions may enhance bulk-solvent proton T2 without population transfer. Heteronuclear spin decoupling suppresses the scalar coupling contribution to solvent 1H T2. The difference in T2 with and without X-1H decoupling may provide image contrast without delays for infusion of contrast agents between data acquisitions. Studies of aqueous solutions of 15N-labeled arginine show that exchange of labile amine protons enhances the bulk-water T2, but the small contribution of scalar-coupling modulation relative to chemical shift effects limits the application of arginine as a novel contrast agent.;The limited lifetime of HypXe polarization restricts applications, while the favorable T1 and sensitivity of SF6 make it a viable alternative as an inert gaseous contrast agent to potentially measure local uptake and washout. Changes in 19F relaxation rates from 19F-1H inter-nuclear coupling can provide vital steady-state information about aqueous environments. Experimental results indicate that intramolecular interactions dominate SF6 T1 and intermolecular interactions significantly affect T2 and may provide information about local environments.